1. Field of the Invention
The present invention relates to a variable speed drive device for a bicycle. More specifically, the present invention relates to a variable speed drive device for a bicycle adapted to be coupled to a variable speed gearshift device via a transmission member to electrically drive the variable speed gearshift device.
2. Background Information
Japanese Patent No. 3423285 discloses a conventional variable speed drive device used in a bicycle that is configured and arranged to electrically operate driving of a bicycle derailleur, an internal shift hub, or other variable speed gearshift via a shift cable or other transmission member. This conventional variable speed drive device has a case member, a motor installed on the case member, a reduction gear mechanism for slowing rotation of the motor, a cam mechanism linked to the reduction gear mechanism, a rocker link that is rocked by the cam mechanism, and an inner fastener mounted on the rocker link. The rocker link has an arcuate cable winding surface adjacent to the inner fastener to which an inner cable is coupled. The conventional variable speed drive device is also provided with a coil spring member for biasing the inner cable in the tensioning direction.
With such conventional variable speed drive device disclosed in the above mentioned reference, when the motor operates in response to a shift command, the cam mechanism rotates via the reduction gear mechanism. The rotation of the cam mechanism causes the rocker link to rock, letting out or pulling in the inner cable to execute shift operations of a variable speed gearshift device coupled to the inner cable. By imparting biasing force of the coil spring member to the rocker link, even when the level of force of a return spring of the variable speed gearshift device increases, this force will be cancelled out by the biasing force of the coil spring member, thereby minimizing the torque required of the motor in the gearshift operation.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved variable speed drive device for a bicycle. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.